Merge pull request #26661 from adrianludwin/image-pull-policy

Better document default imagePullPolicy behaviour

content/en/docs/concepts/containers/images.md

@@ -49,16 +49,32 @@ Instead, specify a meaningful tag such as `v1.42.0`.
 
 ## Updating images
 
-The default pull policy is `IfNotPresent` which causes the
-{{< glossary_tooltip text="kubelet" term_id="kubelet" >}} to skip
-pulling an image if it already exists. If you would like to always force a pull,
-you can do one of the following:
+When you first create a {{< glossary_tooltip text="Deployment" term_id="deployment" >}},
+{{< glossary_tooltip text="StatefulSet" term_id="statefulset" >}}, Pod, or other
+object that includes a Pod template, then by default the pull policy of all
+containers in that pod will be set to `IfNotPresent` if it is not explicitly
+specified. This policy causes the
+{{< glossary_tooltip text="kubelet" term_id="kubelet" >}} to skip pulling an
+image if it already exists.
+
+If you would like to always force a pull, you can do one of the following:
 
 - set the `imagePullPolicy` of the container to `Always`.
-- omit the `imagePullPolicy` and use `:latest` as the tag for the image to use.
+- omit the `imagePullPolicy` and use `:latest` as the tag for the image to use;
+  Kubernetes will set the policy to `Always`.
 - omit the `imagePullPolicy` and the tag for the image to use.
 - enable the [AlwaysPullImages](/docs/reference/access-authn-authz/admission-controllers/#alwayspullimages) admission controller.
 
+{{< note >}}
+The value of `imagePullPolicy` of the container is always set when the object is
+first _created_, and is not updated if the image's tag later changes.
+
+For example, if you create a Deployment with an image whose tag is _not_
+`:latest`, and later update that Deployment's image to a `:latest` tag, the
+`imagePullPolicy` field will _not_ change to `Always`. You must manually change
+the pull policy of any object after its initial creation.
+{{< /note >}}
+
 When `imagePullPolicy` is defined without a specific value, it is also set to `Always`.
 
 ## Multi-architecture images with image indexes